This transaction is contained in two MainChain-Blocks:
On Blockexplorer there is a note of this anomaly:
As I understand, those 50 BTC are lost because only one of the rewards can be redeemed.
If so there will never be 21 million Bitcoin available, because those, or more of this sort, are missing?
This is a known bug in the early days of bitcoin.
Was fixed by BIP-30 https://github.com/bitcoin/bips/blob/master/bip-0030.mediawiki
There is a discussion here: https://bitcointalk.org/index.php?topic=216938
And yes, 50+50 bitcoins are missed forever.
In fact, there are much more missed bitcoins. For example, 2500 bitcoins were gone to nowhere in block 0000000000000449ee5b94ba7a051caffff5c23d6a03335f6e20e3985b5ffa61
this is mine that i won in a lottery freebitcoin round 198 last march 2019